Latent Heat Calculator
Heat needed to melt, freeze, boil or condense a mass of water, ice or other substances — Q = mL — with time at a given heating power.
How it works
Q = m × L (no temperature change during the phase change)
During melting or boiling the temperature stays fixed while energy goes into breaking intermolecular bonds — that hidden energy is the latent heat. Water’s values are unusually large: boiling a kilogram takes 2,260 kJ, almost seven times what melting it needs and over five times what heating it from 0 to 100 °C takes. The same energy is released when steam condenses, which is why steam burns are so severe.
Worked example
Boiling 2 kg of water: 2 × 2,260 = 4,520 kJ; at 2 kW that is 37.7 minutes.
Frequently asked questions
Does this include heating up to the boiling point?
No — add m·c·ΔT (specific heat calculator) for the temperature change before and after.
Why is fusion so much smaller than vaporisation?
Melting only loosens the lattice; boiling has to separate molecules completely against all their attractions.
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This calculator is for educational purposes. Double-check important results before acting on them.